Apparatus and method for forming silica glass elements

Abstract

The forming apparatus has top and bottom die assemblies which form a heated silica glass material by press forming. These top and bottom die assemblies include, respectively, mold dies, which are made of isotropic carbon, and core molds, which are made of vitrified carbon. The heating and pressing time of a silica glass element, which requires a high forming temperature, is shortened by pinching the silica glass material between top and bottom core molds by controlling a torque so as to produce a close contact condition which permits heat transfer from the top and bottom core molds to the silica glass material between the top and bottom core molds.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-298087, filed Sep. 27, 2001, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates to an apparatus and a method for forming silica glass elements in which the shortening of the heating time of a glass material for forming is particularly aimed at.[0004]2. Description of the Related Art[0005]Methods for manufacturing glass elements such as glass lenses that are required to provide high accuracy are broadly divided into two: a method which involves forming optical surfaces by grinding and polishing a glass material and a method by reheat pressing. Glass elements are often manufactured by the former method.[0006]In the former method, however, a dozen or so steps are required for forming curved surfaces by grinding and pol...

AI Technical Summary

Benefits of technology

[0010]It is an object of the invention to shorten the heating and pressing time during the forming, by reheat pressing, of a silica glass element which requires a high forming temperature in the forming.

[0011]Another object of the invention is to improve the thermal conductivity from top and bottom die assemblies to a silica glass material in order to shorten the heating and pressing time.

[0012]A further object of the invention is to improve combinations of the materials for top and bottom core molds and top and bottom mold dies surrounding the periphery thereof that constitute top and bottom core mold in order to improve the thermal conductivity from the top and bottom core molds to the silica glass material.

[0013]Still a further object of the invention is to improve the condition of contact between the top and bottom core molds and the silica glass material in order to improve the thermal conductivity from the top and bottom core molds to the silica glass material.

[0023]According to the invention, in a device for heating and press forming silica glass elements, top and bottom mold dies (or drum die) of isotropic carbon and top and bottom core molds of vitrified carbon are used. Because isotropic carbon has a high thermal conductivity and the resistance to thermal shock is also good, the heating and pressing time can be shortened by using mold dies of this material. On the other hand, vitrified carbon has the following features. For example, this material has good heat resistance, can produce hard mirror surfaces, and is less apt to cause a reaction with silica glass. However, because vitrified carbon has a thermal conductivity lower than that of isotropic carbon, heat transfer from the mold dies of isotropic carbon is bad. In the invention, therefore, heating is performed with the silica glass material pinched between a pair of top and bottom core molds in a close contact condition which permits heat transfer. This can shorten the heating and pressing time remarkably and prevent devitrification reliably due to the crystallization of silica glass.

Problems solved by technology

In addition, there arises a problem that large amounts of glass grinding dust harmful to workers are generated.

Moreover, the former method has another problem that it is difficult to manufacture high-value added glass elements having optical surfaces of aspherical surface shape with the same accuracy and in large quantities.

However, when silica glass elements are formed by the above-described manufacturing method by repeat pressing, the following problems exist awaiting solutions.

Moreover, a silica glass material has a problem that the material devitrifies due to crystallization when exposed to high temperatures of not less than 1200° C. for a long time.

Because a glass element which has devitrified cannot be used as an optical element, in reheat pressing it becomes necessary to shorten the heating and pressing time.

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